Question

A ray of light is incident on a plane mirror with a angle of incidence 30 degrees. the deviation suffered by incident ray is

Answer 1

Answer: A ray of light is incident on a plane mirror at an angle of    

We want to determine the angle of deviation.

Explanation:

Question fails to specify if the angle of the incident ray is to the mirror or to the normal.

If we read that to refer to “the angle of incidence” then that is the angle to the normal.

30deg incidence means 30deg reflection … from the normal.

The angle the ray deviates from it’s course, though, is not the same as the angle of incidence or of reflection.

You can work it out from a sketch … draw in a dotted line that continues the original path of the ray, as if the mirror were not there.

Then it is a matter of adding up the angles between the dotted line and the reflected ray.